1. Field of the Disclosure
The present invention is generally related to image sensors, and more specifically, the present invention is directed to high dynamic range image sensors.
2. Background
Standard image sensors have a limited dynamic range of approximately 60 to 70 dB. However, the luminance dynamic range of the real world is much larger. Natural scenes often span a range of 90 dB and over. In order to capture the highlights and shadows simultaneously, HDR technologies have been used in image sensors to increase the captured dynamic range. The most common techniques to increase dynamic range is to merge multiple exposures captured with standard (low dynamic range) image sensors into a single linear HDR image, which has much larger dynamic range than a single exposure image.
One of the most common HDR sensor solutions would be having multiple exposures into one single image sensor. With different exposure integration times or different sensitivities (for example by inserting neutral density filters), one image sensor could have 2, 3, 4 or even more different exposures in a single image sensor. Multiple exposure images are available in a single shot using this HDR image sensor. However, overall image resolution is decreased using this HDR sensor compared to a normal full resolution image sensor. For example, for an HDR sensor that combines 4 different exposures in one image sensor, each HDR image would be only a quarter resolution of the full resolution image.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.